Pin(2)-Symmetry in Monopole Floer Homology

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The main focus of this National Science Foundation funded project is the interaction between two areas of research known as gauge theory and low-dimensional topology. The former is the language in which many physical theories are formulated, while the latter studies the shapes of three- and four-dimensional spaces. It is common to apply knowledge of geometry to predict the behavior of physical systems. For example, it is straightforward to predict the sound of a drum from its shape. The opposite approach is sometimes also feasible; in particular, the study of differential equations originating from gauge theories can lead to very deep insights about the topology of spaces. In recent ground-breaking work, Ciprian Manolescu disproved the almost hundred-year-old Triangulation conjecture, which roughly asserted that in higher dimensions, every space can be cut into very simple pieces. The main goal of this project is to use the PI's recently developed computational techniques to understand in greater detail several properties of the object studied by Manolescu, called the three-dimensional homology cobordism group.This project has two main goals. First, to explore the properties of Pin(2)-monopole Floer homology, a package of invariants of three-manifolds defined in analogy to Manolescu's construction within the Morse-theoretic framework of Kronheimer and Mrowka. The Pin(2)-symmetry is reflected in an extremely rich A-infinity structure on these invariants, and we will focus on understanding the higher operations and their implications for natural topological operations such as connected sums. Second, to apply these tools to study problems in low-dimensional topology, focusing particularly on the homology cobordism group in dimension three. Very little is known about this group, especially regarding the existence of torsion, and Pin(2)-monopole Floer homology may provide an avenue to solve many of these problems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.